An image forming apparatus using an electrophotographic technique is provided with a fixing device for fixing a toner image formed on a recording material on the recording material. The most prevailing method used in the fixing device is a contact heat pressure fixing method in which the toner image is heated and fixed on the recording material while the recording material bearing the toner image is being nipped at a nip portion and conveyed. It is inevitable for the contact heat pressure fixing method to cause a phenomenon of an offset that a part of a toner layer adheres to a fixing roller.
The offset includes several types. A low temperature offset refers to a phenomenon that heat quantity applied to the toner is not enough to sufficiently melt the toner, the toner is not fixed on the recording material, and thereby the toner offsets to the fixing roller. A high temperature offset refers to a phenomenon that heat quantity applied to the toner is excessive to cause the toner to scorch and stick to the fixing roller, and the toner layer is separated.
Other than those above, an electrostatic offset exists. Those offsets cause such problems that surfaces on the front and back sides of the recording material are dirtied from a short-term viewpoint, and an offset toner is accumulated to cause dirty images, cause a failure in the conveyance of the recording material, and shorten the lifetime of the fixing device from a long-term viewpoint.
A toner including a mold release wax has been proposed to prevent the offset phenomenon. The mold release wax is included in the toner, and moved to an interface between a melting toner and the fixing roller in heating and fixing the toner. That prevents the melting toner layer from being separated toward the fixing roller side, and an offset resistance is improved.
The mold release wax included in the toner is liquefied in heating and fixing the toner and a part thereof is vaporized. “A component vaporized from the wax,” which is cooled immediately after vaporization, is solidified again to be moved along with wind flowing in the image forming apparatus. A solidified wax component is liquefied again at a place high in temperature in the apparatus, and adheres thereto.
A place being in contact with the recording material tends to be high in temperature in the image forming apparatus. In other words, the wax component tends to adhere to a conveyance guide and a conveyance roller for the recording material. The adhesion of the wax component to the conveyance guide and the conveyance roller for the recording material hinders the recording material from being conveyed or decreases a friction coefficient of the conveyance roller.
The temperature setting of a heater in the fixing device tends to become higher to meet the demand for an increase in an image forming processing speed. Along with that, the amount of components vaporized from the mold release wax also increases, which may frequently cause the phenomenon that the aforementioned mold release wax component adheres to various places in the image forming apparatus. For this reason, it is important to develop a technique to collect components vaporized from the wax to prevent the components from adhering to various places in the image forming apparatus.
Japanese Patent Application Laid-Open No. 2004-151240 discusses a technique for an absorption sheet for collecting oil (wax), which adheres to the inner face of frame of the fixing device and then drips down.
Japanese Patent Application Laid-Open No. 2008-185878 discusses a technique in which short fibers (aramid fibers) absorbing vaporized wax are planted in the inner face of housing of the fixing device to hold the wax.